1. Field of the Invention
The present invention relates to an evaluation method of IG effectivity in semiconductor silicon substrates and, more particularly, to an evaluation method of IG effectivity on Cu in semiconductor silicon substrates used as substrates for semiconductor devices of various kinds.
2. Description of the Relevant Art
In a ULSI device manufacturing operation, a variety of heat treatments are conducted in various kinds of process steps according to the construction of the device. The presence of contamination with heavy metals, typically Fe, Ni and Cu in these steps of heat treatment causes the formation of defects or electrical levels in proximity to the surface of the semiconductor silicon substrate, resulting in degradation of device characteristics. Therefore, it is necessary to remove such heavy metals in the vicinity of the semiconductor silicon substrate surface which is a region for forming the device before going to the device manufacturing operation. As gettering methods of the heavy metals, IG (Intrinsic Gettering), EG (Extrinsic Gettering) of various kinds and the like are adopted.
It has been long known that the IG effectivity in the semiconductor silicon substrate has a correlation with the amount of oxygen precipitates. Hitherto, the IG effectivity in the semiconductor silicon substrate has been evaluated by measuring the density of oxygen precipitates after selective etching, or measuring the amount of oxygen precipitation from the difference in the amount of infrared absorption (xcex94[Oi]) before and after heat treatment, or the like.
However, the recent device process has been shifting from a conventional high-temperature process to a low-temperature process. Since the growth of oxygen precipitates is retarded in the low-temperature process, it has been difficult to obtain oxygen precipitates of large size sufficient to be observed by a conventional observation technique of oxygen precipitates in high density in the recent device process.
Therefore, the IG effectivity estimated by a conventional observation technique of oxygen precipitates such as a method wherein oxygen precipitates are observed using an optical microscope after selective etching to measure the density of oxygen precipitates (defects), or a method wherein the amount of oxygen precipitates is measured from the difference in the amount of infrared absorption (xcex94[Oi]) before and after heat treatment, does not have a strong correlation with an actual IG effectivity in the case of a semiconductor silicon substrate which passed the low-temperature process.
As a reason for this, the following is presumed: in the low-temperature process, a large number of minute oxygen precipitates (defects) which are difficult to detect by a conventional observation using an optical microscope after selective etching or an observation using a transmission electron microscope (TEM) are generated, and these minute defects contribute to the actual IG effectivity; and the difference in the amount of infrared absorption (xcex94[Oi]) in this case is a much smaller value than a value found in a semiconductor silicon substrate which passed a conventional high-temperature process.
With the above current state, as to a semiconductor silicon substrate which passed a low-temperature process, there is no appropriate evaluation index of an actual IG effectivity at present. In order to evaluate the IG effectivity, there are only two methods: (1) by actually putting a semiconductor silicon substrate to the device process, the influence on the device yield is examined; and (2) by measuring the electrical characteristics such as dielectric breakdown, the IG effectivity is evaluated.
However, in these methods (1) and (2), it is required to put a semiconductor silicon substrate to an actual device process, or a great deal of time, manpower and expenses for manufacturing a MOS device for dielectric breakdown estimation and the like are needed. Therefore, the development of a method whereby an actual IG effectivity can be evaluated at a low cost in a short time has been challenged.
In order to solve the above problem, the present applicants proposed a method for evaluating IG effectivity by whether the relationship Lxc3x97D0.6xe2x89xa71.0xc3x97107 holds, where L (nm) is a diagonal length of oxygen precipitates and D (/cm3) is a density thereof (Japanese Kokai No. 2000-68280).
In the recent device process, Cu has been used as an interconnection material, besides the adoption of a low-temperature process, so that the evaluation index of IG effectivity on Cu contamination resulting from minute oxygen precipitates formed in the low-temperature process has been demanded. The above evaluation method is effective on contamination with Ni or Fe, but in evaluating the IG effectivity on Cu contamination which has recently received attention, there are cases where the IG effectivity on Cu is not actually favorable even if the above relationship is satisfied, or cases where the IG effectivity on Cu is actually favorable even if the above relationship is not satisfied. It is found that the above method is insufficient to evaluate the IG effectivity on Cu with high accuracy.
In order to solve the above problem, an evaluation method of IG effectivity in semiconductor silicon substrates (1) according to the present invention is characterized by experimentally obtaining the optimum ranges of the diagonal length and density of oxygen precipitates which make the IG effectivity on Cu favorable in advance, and evaluating the IG effectivity on Cu by whether the diagonal length and density of oxygen precipitates fall within the optimum ranges.
Using the above evaluation method of IG effectivity in semiconductor silicon substrates (1), it is possible to find the diagonal length and density of the precipitates from a computer simulation. Therefore, it is unnecessary to put a semiconductor silicon substrate to an actual device process, and also unnecessary to manufacture a MOS device for dielectric breakdown estimation, so that it becomes possible to accurately evaluate an actual IG effectivity on Cu at a low cost in a short time.
An evaluation method of IG effectivity in semiconductor silicon substrates (2) according to the present invention is characterized by the optimum ranges, being ranges in which L becomes larger than 300 nm when a value of D is smaller than 1xc3x97109/cm3, and L becomes larger than 200 nm when a value of D is not less than 1xc3x97109/cm3, where L (nm) is a diagonal length of the oxygen precipitates and D (/cm3) is a density thereof in the above evaluation method of IG effectivity in semiconductor silicon substrates (1).
Using the above evaluation method of IG effectivity in semiconductor silicon substrates (2), it becomes possible to very accurately evaluate the IG effectivity on Cu with the range which satisfies the above optimum ranges as the control index.
An evaluation method of IG effectivity in semiconductor silicon substrates (3) according to the present invention is characterized by obtaining the diagonal length and density of the oxygen precipitates from a computer simulation using Fokker-Planck equations with heat treatment conditions input, and then evaluating the IG effectivity on Cu by whether the diagonal length and density fall within the optimum ranges thereof in the above evaluation method of IG effectivity in semiconductor silicon substrates (1) or (2).
Using the above evaluation method of IG effectivity in semiconductor silicon substrates (3), the diagonal length L (nm) and density D (/cm3) of the oxygen precipitates can be obtained with accuracy through a computer simulation, and it is possible to accurately evaluate an actual IG effectivity on Cu in an extremely short time.